1. Field of the Invention
The present invention relates to a heat resistant electrically conductive plastic sheet which comprises a base material layer A comprising three components of a polyphenylene ether resin (hereinafter referred to simply as PPE), a high-impact polystyrene resin (hereinafter referred to simply as HI) and a polyolefin resin (hereinafter referred to simply as PO) and an electrically conductive layer B comprising three components of PPE, HI and an electrical conductivity-imparting material, integrally laminated on one side or both sides of the base material layer A by coextrusion, and a packaging container for a semiconductor integrated circuit (hereinafter referred to simply as a heat resistant electrically conductive carrier tape) obtained by subjecting the sheet to embossing treatment.
2. Discussion of Background
As a packaging for IC or for parts of electronic equipments employing IC, a soft tray, an embossed carrier tape or the like has been known. The plastic sheet constituting the base material for such a soft tray or an embossed carrier tape usually has high surface resistivity, whereby it is easily electrifiable and is highly likely to impair the function of IC. To overcome this problem, there have been proposed (1) a method of coating an antistatic agent on the surface of the packaging container, (2) a method of coating an electrically conductive paint, and (3) a method of kneading an antistatic agent or carbon black into a usual resin.
On the other hand, as a resin has been used as an IC molding compound and moisture absorption of an IC mold has increased, many troubles such as crack of IC molding compound (generally called packaging crack) and corrosion of wiring have occurred frequently due to rapid moisture removal which takes place at the time of bonding IC to the surface of a circuit substrate. To prevent such troubles, it has been common to carry out predrying at a temperature of from 100.degree. to 150.degree. C. so-called baking, prior to bonding IC to the surface of a circuit substrate.
As a material for a packaging container for such baking, many heat resistant electrically conductive resin compositions have been proposed, and trays injection-molded from such resin compositions are practically used. However, such injection molded trays are not suitable for high speed mounting of IC, since movement of the mounting machine is obliged to be complicated. Further, if conventional heat resistant electrically conductive resin compositions are formed into sheets, there will be a problem such as inadequate strength or inadequate secondary moldability of the sheets. To overcome such problems, Japanese Examined Patent Publication No. 50391/1993 proposes a heat resistant electrically conductive composite plastic sheet having an electrically conductive resin layer laminated on a base material layer composed of a polyphenylene ether resin composition. However, by this method, if carbon black is incorporated to the polyphenylene ether resin, the melt viscosity increases substantially, and there will be a difference in fluidity between the base material resin and the electrically conductive resin during coextrusion, whereby defective lamination of the sheet is likely to result, and the sheet tends to be inadequate in the practical strength. Further, when such a sheet is formed into a carrier tape, the secondary moldability tends to be poor, and the resulting tape tends to be practically inadequate as a heat resistant electrically conductive carrier tape.